The goal of this work is the development of a safe, effective, and affordable vaccine to prevent HIV-1 infection resulting from injection drug use, unprotected sex, and exposure-contaminated blood products. We plan to accomplish this goal by improving a vaccine originally tested in injection drug users, AIDSVAX B/E. This proposal takes advantage of recent discoveries demonstrating that many of the most potent neutralizing antibodies in sera from HIV-1-infected people are directed to glycan-dependent epitopes. The recognition that broadly neutralizing antibodies recognize carbohydrate epitopes is revolutionary, and represents perhaps one of the greatest advances in the history of HIV-1 vaccine development. In this proposal, we plan to use this information to develop new vaccine immunogens consisting of recombinant gp120 and fragments of gp120 (scaffolds) produced with the glycosylation required for the binding of these antibodies. We plan to use these immunogens to improve the efficacy of the AIDSVAX B/E vaccine used in the RV144 and VAX003 clinical trials. Our recent studies showed that this vaccine lacked the carbohydrate structure required for the production of antibodies to this new and important class of epitopes. The key criteria of success in this proposal will be: 1) the identification of immunogens and an immunization regimen able to elicit broadly neutralizing antibodies in laboratory animals with activity similar to the prototypic PG9 monoclonal antibody, and 2) the identification of immunogens able to elicit antibodies to the V1/V2 domain of the type that correlated with protection in the RV144 trial. By improving an existing vaccine with an established record of safety and immunogenicity in more than 15,000 subjects, an existing GMP manufacturing process, and demonstrated efficacy, we believe that years of time and millions of dollars can be saved, compared with the cost of developing a new vaccine from scratch. Other useful information that will result from this proposal includes: 1) determining the best method to elicit antibodies to glycan-dependent epitopes in the V1/V2 domain of gp120; 2) the identification of new glycan-dependent and -independent epitopes in the V1 and V2 domains of gp120; 3) understanding the differences in the magnitude and specificity of antibody responses to V1/V2 domain that led to protection in the RV144 clinical trial and was unable to protect injection drug users in the VAX003 clinical trial, and 4) understanding the prevalence of antibodies to glycan dependent epitopes in people who make antibodies to gp120 as a consequence of immunization or virus infection.